The heir apparent in Louisiana’s 5th District will now face a tougher quest to inherit the kingdom, thanks to a little-known eleventh-hour candidate who has changed the dynamic of next month’s race.

Republicans have always labeled state Sen. Neil Riser as the front-runner to succeed former Rep. Rodney Alexander, who resigned in August. Riser had raised the most money, lined up support from House GOP leadership and hired top staff from the governor’s operation. Not surprisingly, he finished first in the primary on Oct. 19.

Vance McAllister, a Republican pipeline construction company owner with deep pockets and several fast-food franchises, filed his candidacy just hours before the deadline. And he defeated 12 other candidates — including a former congressman and state lawmaker — to win second place in the primary.

Whichever Republican wins the Nov. 16 runoff will be the next member from the 5th District. Louisiana election rules allow two candidates, regardless of party, to proceed from the primary to the final runoff.

On paper, this runoff looks like a typical intraparty race that pits a well-established Republican pol against a GOP outsider. But this time, the narrative isn’t that simple.

Riser boasts big conservative bona fides; meanwhile, McAllister has been forced to defend his position on Obamacare. Riser’s biggest downfall in the contest has been his ties to Alexander and unpopular GOP Gov. Bobby Jindal.

“Neil is pretty solid on his conservative record,” a GOP operative said. “It’s all the people who came around him who are hurting him.”

Alexander has donated to and endorsed Riser’s campaign, joining three other Louisiana Republicans in the House as well as Majority Leader Eric Cantor of Virginia. Jindal’s former top aide, Timmy Teepell, serves as Riser’s chief consultant. (Teepell did not return a request for an interview by press time.)

Two Republicans ousted in the primary —former Rep. Clyde Holloway and state Rep. Jay Morris — had accused Jindal and Alexander of “rigging” the contest to give Riser an advantage in the race. Jindal repeatedly denied that charge in local media reports.

While neither Holloway nor Morris were successful, operatives say their supporters comprise about 18 percent of the electorate. They argued that their supporters would most likely back McAllister over Riser in the runoff — if they vote at all.

That support would be essential for McAllister, who finished 14 points behind Riser in the primary. That will be tough in what Republicans expect to be an extremely low turnout contest.

“I think the runoff is going to be on a compressed time schedule, so it’s going to be challenging for McAllister to come back,” Louisiana GOP Executive Director Jason Dore told CQ Roll Call.

McAllister must also withstand a blitz of negative campaigning from the Riser camp.

Riser’s team has laid the groundwork for an attack strategy against McAllister, who they say has waffled on the call to repeal President Barack Obama’s signature health care law.

“We’re going to focus this race on Neil’s record and on what he’s done,” Riser Communications Director Ryan Cross said. “Vance is waffling and he seems a little bit confused about his own position on Obamacare.”

Cross is referring to McAllister’s comment to a local newspaper earlier this month about repealing the president’s health care law.

“I think we’re honestly past that,” McAllister told The Town Talk of Alexandria, La. “So if we know we have to live with it, let’s make it livable. Find the things that don’t work and fix them.”

Riser’s campaign will have the funds to replay McAllister’s comments throughout paid media. He raised a whopping $561,000 in the primary and ended the pre-primary period with $210,000 in cash on hand. Riser, an adept fundraiser, is also expected to raise more for the runoff.

Operatives say the question that remains is how much money McAllister will spend to counter that onslaught.

McAllister brought in $245,000 for the race — and all but $10,000 of that haul came from his personal funds. McAllister’s team says he will likely continue the trend of self-funding throughout the short runoff period.

“A four-week runoff is very intense,” McAllister adviser Josh Robinson said. “You could argue whether [Riser] had a head start on things. He’s a little more organized than we are. But we feel good about our chances. If we took six weeks to come from last place on top of 12 other candidates, we feel good about what we can do in four.”